At the instance of a major environmental disturbance, it is, of course, prudent to turn off the supply of heating gas at the main valve feeding the premises in question. However, there are many instances when, due to the magnitude or nature of the disturbance, such as major earthquake, the responsible person is unavailable to close the valve, or is distracted by other more visible problems and emergencies. Thus, automatically actuating gas cutoff valves, such as the type illustrated in U.S. Pat. Nos. 4,116,209 and 4,745,939. While such valves work very well for their intended purpose of automatically cutting off gas flow to the premises protected thereby, once such a valve is actuated by natural or manmade disturbance, it is only natural to check for any gas leaks that may have developed downstream of the valve as a result of the same disturbance In the absence of such an automatic cutoff valve, it is also desirable that a gas leak detection device can be used to cut off gas flow to the premises.
Immediately following earthquakes and other natural disturbances such as storms, floods, subsidences, volcanic eruptions and certain manmade disturbances such as explosions, fires, sonic booms, vibrations, new appliance installations, new or additional construction, the need has arisen to check for gas leaks, gas pipe rupture, and the like, in order to locate and stop leaks, and in order to reassure the occupants that gas is not leaking in their homes, businesses, industries, schools, hospitals and other buildings. For example, for weeks after a sizeable earthquake, the gas company employees are still locating and repairing leaks in gas lines and are only restoring gas delivery service after it has been ascertained that the leaks are repaired or that there are no leaks present. A considerable time delay is thereby incurred in service restoration.
The main line gas supply should not be used to monitor and detect leaks for safety reasons. Following a disturbance causing the main gas supply to be shut off, the flow meter indicators in the main line drop significantly. In order to use the main gas supply to check for leaks, all applicances would have to be shut off, the high pressure main gas supply would be turned on, and a considerable amount of the high pressure gas would have to be introduced into the line until stabilization of the meter indicators occurred. In the presence of a leak, the high pressure gas would escape into the atmosphere and present a danger of an explosion. Apparatus to detect leaks has commonly employed inert materials for safety reasons.
In non-earthquake prone parts of the world there is often urgent need to check for leaks due to ground settling, flood damage and other vibrational and disruptive causes. A variety of devices and methods have been proposed in the prior art for detecting gas leaks. A fairly elaborate electromechanical valving system providing an electrical alarm signal is disclosed in the Evans U.S. Pat. No. 3,624,627.
The MacMurray U.S. Pat. No. 3,756,072 discloses a portable leak test instrument which is adapted to be installed temporarily and used to check for leaks. The device includes a an air tank, pressure regulator two valves, two pressure indicators and flexible hoses connected via fast disconnect fittings to a stub pipe.
The Ross et al. U.S. Pat. No. 2,727,383 describes a method and apparatus for testing and cleaning pipe lines. Bottled inert gas, such as carbon dioxide, is fed through a flexible hose, coupling, cutoff valve, pressure regulator and pressure gauge to a pipeline system to be checked for leaks. The gas is selected so that any leakage of the gas at a leak site will cause atmospheric moisture adjacent thereto to freeze on the pipe, thereby providing a visible indication of the location of the leak.
The Stern U.S. Pat. No. 2,430,034 describes apparatus for locating leaks via a structure which is inserted into a pipe line. External fluid from a source is piped into one or the other side of the line. A pressure gauge provided on each side of the line indicates whether the pressure is diminishing, thereby signalling a leak.
A major disadvantage of the portable gas leakage detectors is the necessity for opening the gas line in order to install the detector. Explosive gases may be released, even with reduced gas pressure in the line.
The U.S. Pat. No. 3,184,958 to Eaton describes apparatus designed to detect leaks in a coaxial pipe line, such as a subterranean steam pipe line which would be subject to corrosion from intrusion of ground water. Gas is added to the outer cylindrical space between the two pipes at a pressure sufficient to prevent ground water intrusion. When gas is required to be added to the outer space, an alarm signals the detection of a leak.
Applicant's co-pending U.S. Pat. application No. 07/321,960, now U.S. Pat. No. 4,895,018, issued on Jan. 23,1990, provides a permanently installed in-line leak detection unit with an internal pressure gauge to enable continuous-in-line monitoring of pressure. The unit includes a cover to protect the pressure gauge and may either use the gas existing in the main line to monitor pressure or may include an external charging gas source to ascertain leaks.
Heretofore, there has been no practical, low cost, safe and permanently emplaced device that uses existing material stock for aiding a building owner or occupier in monitoring gas pressure to determine whether or not there are any gas leaks following a major disturbance of the type historically likely to cause gas leaks and resultant fires or explosions.